The UK government ratcheted up the criticism after the duo accused of poisoning five Britons – and killing one of them – had appeared on broadcaster Russia Today to claim they had been in Salisbury to visit a cathedral which they described as “famous for its 123-metre spire”.

The pair, who identified themselves as Alexander Petrov and Ruslan Boshirov, said they had come forward to clear their names and insisted they had visited the “wonderful” English city as tourists in an interview released on Thursday morning.

They said that while they may have approached the house of former spy Sergei Skripal by accident on 4 March, they did not carry any poison or commit any crime. While they walked around Salisbury, Boshirov added, the two men “maybe approached Skripal’s house, but we didn’t know where it was located”.

Downing Street responded a few hours later. The prime minister’s official spokesman said that the interview contained “lies and blatant fabrications” that “are an insult to the public’s intelligence”. He added: “More importantly, they are deeply offensive to the victims and loved ones of this horrific attack.”

The spokesman added: “An illegal chemical weapon has been used on the streets of this country. We have seen four people left seriously ill in hospital and an innocent woman has died. Russia has responded with contempt.”

Diplomatic relations between the two countries have been strained in the past 48 hours after Vladimir Putin said on Wednesday Russia had identified the two men accused by the UK of being spies who had carried out the Salisbury poisoning. The Russian president said they were civilians and called for them to come forward.

A day later the two men, visibly nervous, appeared on RT. Over 25 minutes they gave cursory details of a two-day trip to the UK.

Petrov and Boshirov confirmed that they were two men shown in stills from CCTV cameras released by British police investigating the attempted murder of Skripal, a Russian ex-spy who passed information to the British.

The man who identified himself on air as Petrov said of Salisbury: “Our friends had been suggesting for a long time that we visit this wonderful town.”

Boshirov said the two had gone to visit Salisbury Cathedral, “famous not just in Europe, but in the whole world. It’s famous for its 123-metre spire, it’s famous for its clock, the first one [of its kind] ever created in the world, which is still working”.

While they walked around Salisbury, he added, the two men “maybe approached Skripal’s house, but we didn’t know where it was located”.

Skripal’s home is almost two miles from the cathedral and nowhere near other attractions they say they were interested in, including Old Sarum and Stonehenge.

The description of the cathedral, with its 123-metre spire and the oldest working clock in the world, appeared to have come directly from its Wikipedia entry. He also referred to it as the “cathedral of the blessed Virgin Mary”, a phrase not commonly used in modern-day Salisbury, but one used in Wikipedia.

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The pair confirmed they visited Salisbury twice, on 3 and 4 March. British police say the first brief visit was designed to stake out the city in advance of the attack. Petrov said that they turned back that day because it was cold.

“We arrived in Salisbury on 3 March and tried to walk through the town, but we lasted for only half an hour because it was covered in snow,” Petrov told the RT editor Margarita Simonyan.

“We specifically went there to see the Old Sarum [an ancient settlement near Salisbury], Stonehenge and the cathedral and decided to finish this thing on 4 March.”

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Boshirov said they only spent an hour in Salisbury on 3 March “mainly because of the lags between trains”. “We were just taking in the English gothic [style],” he said. “Nobody shows that part,” Petrov added, noting the CCTV stills mostly showed the two men at railway stations.

The resulting interview left sceptical Kremlin-watchers wondering whether the suspects’ alibi was a show of defiance by Moscow, a slapdash job by Russian intelligence, or a version of events aimed at a domestic audience.

Investigators say novichok, the nerve agent used in the attack, was transported in a fake Nina Ricci perfume bottle.

Asked about the bottle on Thursday, Boshirov said: “Is it silly for decent lads to have women’s perfume? The customs are checking everything, they would have questions as to why men have women’s perfume in their luggage. We didn’t have it.”

Simonyan asked the men indirectly if they were gay, despite avoiding other questions about their background during the interview.

“Speaking of straight men, all footage features you two together,” she asked. “What do you have in common that you spend so much time together?”

The men declined to respond. Simonyan later tweeted: “I don’t know if they’re gay or not gay. They’re so stylish, as far as I could tell – with their beards and haircuts, tight pants.

“They didn’t come on to me,” she added.

British police say the names used by the men are aliases and there is evidence they are Russian military intelligence agents. They denied this during the interview, although they gave no information about their history or where they live. Nor did they show passports confirming their identities.

The UK said that it wanted to put the two men on trial, but the authorities have said they will not attempt to seek their extradition because Russia does not comply with extradition requests. No 10 said the two were “wanted men” and must be “brought to justice in the UK”.